This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Generally, the present specification relates to mobility of elements within networks and/or communication systems, and to mobility of networks within a communication system. In this regard, by way of example only, reference will hereinafter be made to network environments based on Internet protocol (IP) schemes, as IP is currently deemed to be the most prevailing technology for today's and future communication systems, however without being restricted to the use of IP.
Mobile IP in its currently specified version MIPv6 allows an IPv6 node to maintain its existing connection on a network layer according to the ISO/OSI layer model, while it changes its location and possibly the link to which it is connected. Whenever a node changes its link, it has to get a new topologically correct IPv6 address to stay connected with a packet data network (PDN) such as the Internet. But as soon as an IP address of a node changes, all of the connections that were initiated with the previous IP address will terminate ungracefully, and the node will not be reachable with that previous IP address. However, with the help of Mobile IPv6 a node can maintain its existing connections while it is changing its location and the IP address. Mobile IPv6 accomplishes this by assigning a particular IPv6 address to the node, which is used to initiate all of the communications with that mobile node and through which the mobile node is always reachable. Mobile IPv6 actually provides survivability at the transport layer by maintaining the address at the network.
According to currently used terminology, the following terms will be used hereinafter.                A mobile node (MN) is an Internet-connected device whose location and point of attachment to the Internet (or any other PDN) may frequently be changed. A node's mobility could be a result of physical movement or of changes within the topology.        A correspondent node (CN) is a peer node with which a mobile node is communicating. The correspondent node may be either mobile or stationary.        A home address (HoA) is a relatively permanent IP address given to a mobile node. The home address remains unchanged no matter where the mobile node is located.        A Home agent is a router on a mobile node's home network that maintains information about the device's current location, as identified in its care-of address.        A home network is where a mobile device has its permanent IP address (home address).        A foreign network is any network other than the home network to which a mobile device may be connected.        A care-of-address (CoA) is a temporary IP address for a mobile node that enables message delivery when the device is connecting from somewhere other than its home network.        A binding is an association of the home address of a mobile node with a care-of address for that mobile node, along with the remaining lifetime of that association.        A binding cache is a database that is maintained both at home agent and at correspondent node and consists of binding information of mobile nodes with which they are communicating.        A binding update list is a database (maintained at a mobile node) about all bindings that the mobile node has sent to its home agent and correspondent nodes. This database helps the mobile node to keep track of the lifetime of all bindings so that they can be refreshed before they get expired.        
FIG. 1 shows a basic network topology according to current Mobile IP standards.
There are specified two modes of operation of Mobile IPv6. In the first mode, all communications between a mobile node and a correspondent node takes place via a home agent. This mode of operation is called Bidirectional Tunneling. In contrast thereto, in the second mode of operation called Route Optimization, communications are carried out between a mobile node and a correspondent node without home agent's intervention. These two modes of operation are deemed to be known to the reader of the present specification, and will not be described in detail herein.
In bidirectional tunneling, it is known that due to the tunneling mechanism source and destination IP addresses of IP packets remain intact and transport layer connection can still be maintained. Whenever a mobile node makes a movement, it can register its new care-of address through a binding update message and hence can maintain its existing connections without any problem. Moreover, a mobile node is always reachable through its home address irrespective of the mobile node's actual attachment point to the Internet or any other packet data network.
Furthermore, it is deemed to be known that routing packets through a home agent by way of bidirectional tunneling will add additional delays in communication between a mobile node and a correspondent node. Another drawback of bidirectional tunneling is the introduction of a single point of failure in the network. Still another disadvantage of bidirectional tunneling is that it demands more bandwidth than is actually needed for direct communication between a mobile node and a correspondent node.
Thus, although it is not possible to keep the home agent completely out of the scene, it is preferable to avoid home agent's intervention, i.e. using route optimization. A direct communication between a mobile node and a correspondent node is possible if the home agent informs the correspondent node about the current care-of-address of the mobile node. Once a correspondent node and a mobile node are reachable for each other, they can start direct communication without home agent's involvement. The process of establishing the direct communication is called the Return Routability Procedure (RRP).
Today's widespread use of IP-based applications in portable devices implies a high demand of mobility of entire networks of IP-based devices, instead of mobility of only one node. For this purpose, Mobile IP has been extended to provide basic network mobility support under the name NEMO (Network Mobility). NEMO makes it possible for all devices in a mobile network to have uninterrupted access to a packet data network such as the Internet even when the network changes its point of attachment thereto. Similar to a single mobile node in Mobile IP, all devices in the mobile network are unaware of their network's mobility with the help of NEMO.
Though it is also possible to achieve mobility of a network without the use of NEMO, namely by enabling Mobile IP on all IP-based devices of the network, this would generate excess overheads when every device will have to perform Mobile IP functionality. NEMO actually moves the mobility functionality from a mobile node to a mobile router so that the mobile router can change its point of attachment e.g. to the Internet, which is transparent to all connected device in its mobile network.
According to currently used terminology, the following terms will be used hereinafter.                A mobile router (MR) is a router that can change its point of attachment e.g. to the Internet without disrupting higher layer connections of its attached devices.        An access router (AR) is a router that provides the PDN access to a mobile router. A mobile router usually connects to an access router over a wireless link and hence becomes a part of the network supported by that access router. All incoming and outgoing traffic of a mobile router routes through the access router.        A mobility agent (MA) is any IP device that can perform mobility functionality. It includes a mobile node as well as a home agent.        A mobile network node (MNN) is any IP device that is attached to a mobile network either on permanent basis or as a visitor. A mobile network node will not be aware of network mobility.        
NEMO as currently specified works rather similar to Mobile IP.
Remember that in Mobile IP a mobile node can change its point of attachment to the Internet keeping its existing higher layer connections alive. This is achieved by sending the home agent a binding update message informing about the current location (care-of address) of its mobile node. Once the binding is complete, the home agent intercepts and forwards all traffic destined for the mobile node to the mobile node's care-of address via a tunnel, while the reverse traffic follows the same path, but in opposite direction.
NEMO is basically an extension of Mobile IP enabling an entire network to be mobile so that it can change its point of attachment e.g. to the Internet at any time. In other words, NEMO allows a mobile router to take over the role of a mobile node in performing mobility functions. All the nodes that are connected to this mobile network, termed as mobile network nodes, will neither be aware of network mobility nor are they required to perform any mobility functions themselves. A mobile router will take the responsibility for sending binding updates to their home agents. A mobile router will also send its network's prefix in the binding update so that corresponding home agents can bind an entire network to the mobile router's care-of-address and forward all packets for that network to that mobile router. A mobile router will receive all these packets via tunnels and will simply forward them to its mobile network nodes. NEMO also uses extended Mobile IP signaling messages. This extension includes e.g. a flag (R flag) to indicate that a sender of the message is a mobile router instead of a mobile node. Moreover, extended signaling also has an optional mobile network prefix field which is used to update network prefix information.
FIG. 2 schematically shows the exchange of IP traffic between a correspondent node CN and a mobile network node MNN using NEMO. All the packets from correspondent node CN to the mobile network take their path to the home agent using a standard routing mechanism. The home agent has binding information for the mobile network and hence sends all these packets via a tunnel to the respective mobile router. The tunnel has its end point at the mobile router where the packets are de-tunneled and are forwarded to mobile network node MNN using a standard routing mechanism. Conversely, the traffic that originates from mobile network nodes will take its path to the mobile router, where the packets will be tunneled to the home agent which will then perform the standard routing to forward them to the destination node CN.
According to current NEMO standardization, NEMO introduces a mobile router (MR) concept, wherein the mobile router provides for mobility for the connected mobile network nodes (MNNs) or other mobile routers (MRs), which may lead to the creation of nested structures within the moving network. All incoming and outgoing traffic of MNNs, joining a nested moving network by connecting to the nested MRs, must go through the bi-directional tunnels established between the corresponding MRs and their HAs.
As an example, it is shown in FIG. 3 how traffic of mobile router MR3 is routed via all home agents of the individual mobile routers of the nested moving network. In this way, a packet that originates from a node of MR3 will pass different networks. Namely, the traffic originating from VMR3 is tunneled and routed through home networks of all intermediate nodes. It is noted that the term “mobile router” is also referred to as Visiting Mobile Router (VMR), since these are assumed not to belong to the home network of the top-level mobile router (TLMR) of the nested structure.
Although such an arrangement allows mobile network nodes to reach and be reached ultimately by any node on the Internet or any other packet data network, a lot of problems arise for nested moving networks and their connected mobile network nodes. Such problems include, among others, problems in terms of degradation of network performance (e.g. increase of overhead due to tunneling, increase of transmission delay), problems in terms of network usage (e.g. inefficient use of costly radio resources, inefficient use of network resources), as well as problems in terms of business and administration aspects. In the latter case, an operator (e.g., in FIG. 3 the network operator of TLMR) shall have the means to mandate that all traffic related to its subscribers has to travel through its own network (i.e. through the home network) and not through the other ones (except, of course, the network at which the nodes (i.e., VMRs) are connected and the TLMR's network). This means that the traffic of each VMR goes through its home network and the home network of the TLMR. This restriction imposes the ease of charging for each packet and the deployment of network policies. This means also that the use of Mobile IP Route Optimization in nested NEMO environments is not a suitable solution to reduce the above-mentioned delay and overhead problems. Further, there remain other problems due to network policies of different operators, when processing traffic of visiting nodes (i.e., VMRs) in nested NEMO environments.
As regards the use of route optimization, besides the above, current techniques additionally suffer from the following drawbacks.
Pursuant to a proposed optimized route cache protocol (ORC), there are required significant deployment efforts for dedicated ORC routers that have to be introduced in the networks. Furthermore, such a proposal lacks a routing algorithm and an address management scheme in the moving network.
Pursuant to a proposed Mobile IPv6 route optimization for network mobility (MIRON), there is introduced a new network entity called MAR (MIRON Access Router) in a moving network, thus resulting in inflexibility for a moving network and increasing the complexity of acquiring addresses. Furthermore, such a proposal mandates that a mobile router must maintain state information of every route optimization session for each mobile network node which it serves.
Pursuant to a proposed route optimization in nested mobile network (NEMO) using the optimized link state routing protocol (OLSR), there is not specified any address assignment and/or how to deliver incoming packets.
Pursuant to a proposed packet delivery mechanism between local nodes of the same moving network, local nodes (i.e., local mobile nodes) are of interest and routing in this regard can be seen for outgoing packets sent from local nodes inside the moving network and destined to a another local node that left the same moving network (regardless of whether the moving network is nested or not).
Accordingly, there does not exist any feasible solution to the above drawbacks and problems with respect to network mobility, in particular with respect to network mobility in multi-level networks.